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The latest research in the Journal of Applied Surface Science emphasizes the potential of two-dimensional materials as a means of forming vertical heterostructures that are controlled by van der Waals forces (attractive and repulsive forces between molecules, atoms, and surfaces). ) Keep it together. These two-dimensional heterostructures can be created by directly stacking mechanically peeled sheets of appropriate materials.
Research: Direct growth of graphene-MoS2 heterostructures: customized interfaces for advanced devices, applied surface science. Image Credit: Sashkin/Shutterstock.com
The heteroepitaxial method of crystal growth and material deposition is still one of the most popular and widely used methods for forming a crystal layer on a substrate.
Hetero-epitaxial layers usually provide well-defined orientations. These methods represent an ideal way to grow and integrate thin films of material crystals, otherwise crystals cannot be obtained.
Two-step synthesis. Temperature and partial pressure curve (purple dotted line) using H2 diluent. Temperature: 650 ºC (nucleation and growth), t0=40 minutes, t1=4 minutes, t2=120 minutes, t3=40 minutes. The H2 flow rate is modified between 20-50 sccm. CH4 flow = 2 sccm. Plasma power: 200W. Image source: R. Muñoz et al., Applied Surface Science
Traditional heteroepitaxial growth has significant limitations, and this process is only applicable to materials that exhibit uniform lattice constants. This ensures that interface defects or dislocations that affect performance are kept to a minimum.
Certain 2D heterostructures can be created by directly stacking mechanically peeled sheets of appropriate materials.
These two-dimensional materials have promoted the development of a series of photonic and electronic devices, and it has been found that mechanically exfoliated single-layer and multi-layer graphene sheets have excellent potential for use as high-performance electrodes in heterostructure devices.
When used in room temperature photodetection applications, the effective charge transfer of the mechanically exfoliated graphene-MoS2 heterostructure also leads to unprecedented levels of responsivity and sensitivity.
These applications provide excellent prospects in terms of their performance, applicability and versatility, but so far, the low yield of mechanical peeling methods, time-consuming production processes and opportunities for contamination transfer crystals have hindered their wide application and Scalability.
In order to mitigate these risks and resolve these obstacles to industrialization, it is essential to develop a truly scalable manufacturing method.
With this in mind, advanced technologies for direct heterostructure growth through MoS2/graphene and graphene/MoS2 have been developed. A paper recently published in the journal "Applied Surface Science" proposes a direct synthesis on MoS2 New method of graphene film.
This is done at low temperatures by plasma-assisted chemical vapor deposition (CVD) using CH4 and H2 as precursors. The researchers emphasized that attempts to grow graphene directly on MoS2 are limited due to the need for complex, multi-step protocols that often lead to amorphous carbon deposition.
SEM image of graphene film without S (a), with S (b) and original MoS2 morphology (c). (d) EDX% atomic semi-quantitative analysis of the previous sample. We included C, O, Mo, and S in the quantitative analysis, and normalized the S/Mo ratio = 2 to the value obtained in the original MoS2 single crystal as the standard. Image source: R. Muñoz et al., Applied Surface Science
On the contrary, this new CVD-based method uses a relatively simple two-step synthesis scheme to manage the nucleation and growth stages of the film through different processes, thereby directly synthesizing graphene films on the surface of the exfoliated MoS2 single crystal.
By monitoring and adjusting specific parameters, including temperature, processing time, partial pressure and precursor gas flow, the researchers successfully increased the grain size of graphene and improved the quality of the MoS2 interface.
The researchers also introduced external S substances into the steam to effectively repair the natural or induced S vacancies in the MoS2 substrate and help ensure a more uniform surface.
A series of characterization experiments were conducted to evaluate the healing effect of S on the MoS2 structure. The surface chemical analysis of XPS and the cross-sectional HR-TEM morphology confidently confirmed that the defects or vacancies in the MoS2 substrate were significantly reduced during the synthesis process. S vapor.
Conductive AFM is used to perform a series of graphene conductance measurements, highlighting the influence of the final stoichiometry of MoS2 on its conductance.
Perhaps the most significant advantage of this low-temperature growth is its high scalability. It can also create a clean, chemically controlled graphene-semiconductor interface, which can have multiple uses when integrated into heterostructures used in advanced electronic and photonic devices.
Since the structure and chemical properties of the graphene film grown at its interface with MoS2 can be customized, there is a lot of room for further modification of these synthesis parameters to increase optimization and customization according to specific application requirements.
Plasma-assisted CVD is an inherently scalable method with many advantages, especially due to its relatively simple and effective implementation relative to its mechanically peeled counterparts.
(a, b) High-resolution AFM topographic images of samples deposited with H2 flow (20 sccm-30 sccm), without (a) and with S (b). (c) XPS C 1s core level spectrum of the sample deposited in two steps, using H2 flow (20 sccm-30 sccm), without S (black line) and S (red line). Image source: R. Muñoz et al., Applied Surface Science
Graphene's advantages and potential uses are well documented, especially its application in the semiconductor field, where it is considered a possible successor to silicon in the entire industry.
These processes can also be applied to other semiconductor van der Waals heterostructures, possibly extending their use cases to a range of sectors and industries.
R. Muñoz, E. López-Elvira, C. Munuera, R. Frisenda, C. Sánchez-Sánchez, J. Ángel Martín-Gago, M. García-Hernández, Direct growth of graphene-MoS2 heterostructures: advanced equipment Customized interface, Applied Surface Science (2021), doi: https://www.sciencedirect.com/science/article/pii/S0169433221029019?via=ihub
Benedette Cuffari 2018 AzoMaterials, can graphene change the semiconductor industry? https://www.azom.com/article.aspx?ArticleID=16889
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Adrian Brian Thompson is a freelance writer, educator and creative based in Todmorden, England. His diversified academic and industry background covers many fields from frontline youth and support work to marketing, website development, copywriting, event production and project management. Adrian has a master's degree in music industry studies and is currently studying for a doctorate in music (including politics and social sciences) at the University of Liverpool.
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